This invention relates generally to a tracking lens carrier for an optical sensor carried on an integrated chip (IC) and an assembly integrating the lens carrier into an optical trackball device. More particularly, the invention provides a tracking lens carrier which snaps onto the IC such that the aperture plate of the IC bears against the carrier and the lens registers and aligns with the optical sensor. In a trackball environment the lens carrier is also aligned with the tracking aperture of a ball cup.
Integrated chips with optical sensors are typically used for solid state computer input devices which rely on optical tracking to calculate relative displacement values to be communicated to an output converter. These input devices include optical pointing devices such as computer mice and trackballs. An IC with a reflective optical sensor is commercially available from Hewlett-Packard under the designation HDNS-2000, and is typically mounted on a printed circuit board (PCB). which is assembled with a lens plate. The assembly is mounted on a base plate of a housing for the computer input device. The base plate has an aperture operatively registered with and aligned with the magnified light from an LED for the optical sensor. Conventional assemblies of these components have relied on simple registration tabs and mating in the base plate, lens plate and IC mounted PCB to ensure that the aperture plate of the optical sensor, lens and aperture are operatively aligned.
With multiple components which must be assembled and registered together, any misalignment or registration error in such a conventional assembly is compounded and results in an unreliable or even inoperable pointing device. This can be a particular problem during manufacture since these components of pointing devices are most often assembled by hand.
Due to the multiplicity of parts which must be registered and assembled together these conventional assemblies are inefficient to manufacture and suffer from reliability flaws. With currently employed parts and techniques, there is no reliable way of ensuring repeatable and precise registration of the lens and base plate aperture with the aperture plate of the IC optical sensor.
In both optical mouse and trackball type devices, the lens must be aligned with a tracking aperture through which light is supplied to enable the optical sensor to xe2x80x9creadxe2x80x9d a pattern on a tracking surface. The tracking surface is a flat surface for an optical mouse or a ball for an optical trackball. In conventional optical input devices, the tracking aperture is a through-hole which provides an avenue for contaminants such as dust or other particles to enter the device housing.
In optical trackball devices the ball itself presents the tracking surface that is xe2x80x9creadxe2x80x9d by the optical sensor. For typical optical trackballs, the ball is placed in a socket on the top of the housing or along a side of the housing for manipulation by a user""s finger or thumb. A drawback of the conventional optical trackball devices is that the optics or the lens and the electronics including the sensor are extremely sensitive to dust, dirt, liquid spills and other contaminants. With the ball socket located at the top or on the side of the housing makes the device components more susceptible to contaminants since contaminants can fall down easily into the socket and accumulate on the sensor.
The present invention overcomes the problems of the prior art by providing a lens carrier with retaining legs which structurally affix the lens to the IC in such a manner as to automatically align and register the lens with the aperture plate of the optical sensor. The retaining legs of the lens carrier are resilient to enable the carrier to snap-on to the IC, and thus attached, the IC and lens function as an integral unit when assembled with the remaining components of the pointing device. By attaching the IC and lens in this manner the optical sensor and the lens are in fixed relation to one another and repeatedly precise registration of parts is ensured.
The snap-on lens carrier has a body portion which includes the lens and retaining legs arranged on the ends of the body portion. The retaining legs may take various forms, but in general are perpendicular to the body portion with a retaining detent formed at each of their free ends. The retaining legs are configured so that their length between a bearing area on the body portion and the detent corresponds to the thickness of an optical sensor IC. When the snap-on lens carrier is assembled to the IC, in a cradle-like manner, the body portion of the carrier bears against a flat side of the IC so that the IC aperture plate is aligned and registered with the lens with each retaining leg extending along an end of the IC and affixed thereto by the detents bearing against the opposite side of the IC.
In order to take maximum advantage of the inventive lens carrier in a pointing device assembly, the PCB is configured to receive the optical sensor IC and includes sufficient openings for the retaining legs of the lens carrier to protrude through the PCB and attach to the IC. Once the IC is mounted to one side of the PCB, the lens carrier is positioned from the opposite side of the PCB with its retaining legs extending through assembly openings to snap onto the IC and provide automatic alignment and registration of the lens with the optical sensor. By affixing the IC to the lens carrier in this manner, several registration and alignment issues during the assembly process are nullified, and precision and repeatability are enhanced.
The snap-on lens carrier is adapted to be used in both optical mouse and optical trackball environments. Another aspect of the assembly for trackball devices is the provision of a ball cup to line the socket. The ball cup completely supports the ball and surrounds the portion of the ball received therein. The cup includes a tracking aperture having an integral window pane to keep out contaminants and provide higher electrostatic discharge protection to the components. The cup also includes alignment guides for attaching a PCB having an optical sensor IC and snap-on lens carrier mounted thereon. The snap-on lens carrier ensures that the optical components are automatically aligned with the tracking window of the ball cup.